1. Field of the Invention
The present invention relates to a solid-state imaging device using a charge coupled device (hereinafter, referred to as the CCD), and in particular, to a solid-state imaging device using a CCD which is molded with a transparent resin. Hereinafter, the solid-state imaging device using a CCD will be referred to as a CCD solid-state imaging device.
2. Description of the Related Art
As an example of a packaged CCD solid-state imaging device, a clear-mold CCD solid-state imaging device which is molded with a transparent resin has actively been developed.
FIG. 4 is a schematic cross sectional view of a conventional clear-mold CCD solid-state imaging device 40 which is molded with a transparent resin 20. The clear-mold CCD solid-state imaging device 40 includes a one-chip CCD solid-state imaging device 10 and an input/output terminal 30. A surface of the one-chip CCD solid-state imaging device 10, the surface having a light receiving section, is covered with a transparent passivation film 17 formed of silicon oxide, silicon nitride, or the like. The one-chip CCD solid-state imaging device 10 is entirely covered with the transparent resin 20 formed of a heat-curing resin such as an epoxy resin. The transparent resin 20 is provided in order to protect the one-chip CCD solid-state imaging device 10 from an external physical impact and also from moisture and oxide in the air.
FIG. 3 is a cross sectional view of the one-chip CCD solid-state imaging device 10 and a vicinity thereof. The one-chip CCD solid-state imaging device 10 includes a semiconductor substrate 11, a plurality of photodiodes 12 arranged in a matrix (namely, in a plurality of rows), and CCDs 13 respectively provided adjacent to the rows of the photodiodes 12. The photodiodes 12 each act as a light receiving section. A silicon oxide film 14 is provided on the semiconductor substrate 11 so as to cover the photodiodes 12 and the CCDs 13. Two polysilicon electrodes 15 are provided in a stack above each CCD 13. Each CCD 13 and the two polysilicon electrodes 15 constitute a transfer section 21. Incident light is converted into electric charges, and the electric charges are transferred through the transfer section 21 to another transfer section (not shown) provided perpendicular to the CCDs 13. Light shielding films 16 formed of aluminum or the like are provided on areas of a surface of the silicon oxide film 14, the areas being above the polysilicon electrodes 15. The light shielding films 16 are protected by the transparent passivation film 17 laminated on the silicon oxide film 14.
The one-chip CCD solid-state imaging device 10 having the above-mentioned construction is entirely covered with the transparent resin 20 to produce the clear-mold CCD solid-state imaging device 40.
A camera including the clear-mold CCD solid-state imaging device 40 was continuously operated at a temperature in the range of 60.degree. C. to 90.degree. C. and a relative humidity of 30% or lower. In approximately 70 to 100 hours, a black defect was generated in an obtained image. The black defect is a black point or a diversity in brightness generated in an image obtained by a CCD solid-state imaging device.
The black defect is considered to be generated for the following reason.
The transparent resin 20 covering the one-chip CCD solid-state imaging device 10 includes impurity ions such as a fragment of a polymerization initiator. The impurity ions known as moving ions are uniformly distributed in the transparent resin 20. When the transparent resin 20 is heated to a high temperature, the moving ions can easily move in the transparent resin 20. When the clear-mold CCD solid-state imaging device 40 is operated at a high temperature, the moving ions are excited by electric charges generated on a surface of the light receiving section of the one-chip CCD solid-state imaging device 10, thereby gathering to a vicinity of an interface of the transparent resin 20 and the transparent passivation film 17. However, the moving ions, which move slowly in the transparent resin 20, cannot move sufficiently fast in response to a change in the electric charges occurring at the light receiving section. Accordingly, the electric charges of the moving ions undesirably remaining in the vicinity of the interface influence the electric charges generated in the light receiving section. In consequence, the electric charges in the light receiving section are not completely transferred to the CCD 13, or electric charges cannot be generated in accordance with an intensity of incident light. Thus, the black defect is generated.
It was confirmed that the black defect is deleted by stopping the operation of the camera and leaving the clear-mold CCD solid-state imaging device 40 at a temperature in the range of 70.degree. C. to 80.degree. C. Such a phenomenon is considered to occur because the moving ions are dissipated all over the transparent resin 20 from the interface thereof with the transparent passivation film 17.